Conductor strip arrangement for a molded electronic component and process for molding

ABSTRACT

In the case of molded electronic components a mold material ridge remains in the separation plane of the mold tool. This is particularly disadvantageous if the ridge leads through a surface area of the housing, serving as a docking surface for a suction needle.  
     Manufacturing process and conductor strip arrangement for a molded electronic component where at least one semiconductor element is located on an electrically conducting conductor strip, and where around the conductor strip and the at least one semiconductor element a housing made of a molding material is arranged such that there are still sections of the conductor strip outside the housing. A characteristic feature is that sections of the conductor strip are enlarged in some sections such that these enlarged sections are directly adjacent to the later housing or even protrude into the housing in order to prevent the formation of a ridge.  
     The invention is particularly suitable for the production of molded electronic components whose separation plane runs through that housing surface which serves as docking surface for a suction needle.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a conductor strip arrangement for a molded electronic component where at least one semiconductor element is located on an electrically conducting conductor strip, and where around the conductor strip and the at least one semiconductor element a housing made of a molding material is arranged such that there are still sections of the conductor strip outside the housing, and a process for molding a housing of an electronic component in a mold form, with the component featuring an electrically conducting conductor strip and connection pins located to one side, and the conductor strip having a frame with frame sections, which forms the lateral boundary between the top and bottom sections of the mold form and whose diameter essentially is slightly larger than the diameter of the actual mold form.

[0002] Such a molded electronic component is known, for example, from the German patent publication DE 196 53 054 A1. In the case of such molded electronic components, semiconductor chips (optoelectronic transmitter and receiver, integrated circuit for signal processing) are first glued or soldered by machine onto a metal conductor strip and then contacted to one another and with the conductor strip by means of thin gold or aluminum wires. Then, using a mold process, semiconductor chips and conductor strips will in most cases be enveloped by means of a thermoplastic material such as a synthetic resin, for example, thereby creating a housing for the protection of this assembly.

[0003] When the housing is manufactured, there remains an edge or protrusion of mold material in the separation plane of the mold form, between the top and bottom sections, which edge is also designated as a “ridge”. This is particularly disadvantageous if the ridge runs through that surface of the housing which a suction needle from an automatic assembly machine will be docking onto at a later time, in order to take up the component and place the same onto a printed circuit board, for instance. Due to the ridge the suction needle does not connect tightly but draws in a great deal of external air, thus causing insufficient holding suction for any component to be taken up. In addition, when it is taken up the component will tilt over and assume a tilted and non-definable position on the suction needle. For this reason, an unacceptably large number of components are lost during transportation or are positioned imprecisely.

[0004] It is therefore attempted to keep the ridge as small as possible; however, this requires mold tools with very strict tolerances, very precise manufacturing, and additional controls. But these measures lead to significantly increased manufacturing costs without the problem having been really solved.

SUMMARY OF THE INVENTION

[0005] The invention is based on the task to state and design a conductor strip arrangement for a molded electronic component according to the preamble of claim 1 such that it can be taken up without difficulty by an automatic assembly machine and placed on a printed circuit board. It is furthermore the task of the invention to state a process for molding such an electronic component.

[0006] According to the invention, this task is solved by a conductor strip arrangement stated in patent claim 1 and a molding process with the characterizing features of patent claim 5.

[0007] The molded electronic components manufactured in accordance with claim 5 feature the advantage that they can be taken up without difficulty, held securely and placed exactly, by automatic assembly machines without particularly strict tolerances having to be maintained during the production of the molded electronic component or any specials tools having to be used for its production.

[0008] The invention is particularly suitable for the production of electronic components whose separation plane runs through that housing surface which serves as docking surface for a suction needle from an assembly machine.

[0009] Advantageous further embodiments of the conductor strip arrangement according to claim 1 and the molding process according to claim 5 are stated in the sub-claims.

[0010] In the following the invention will be explained by means of an embodiment example and the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1: a top view of an assembly consisting of a conductor strip already populated with contacted semiconductor components,

[0012]FIG. 2a: a top view of an electronic component which comprises the assembly according to FIG. 1 and is additionally provided with a housing,

[0013]FIG. 2b: a side view onto the electronic component according to FIG. 2a,

[0014]FIG. 3: a side view onto the electronic component according to FIGS. 2a and 2 b during a subsequent production step,

[0015]FIG. 4: the electronic component finished in accordance with the process stated by the invention, and

[0016]FIG. 5: an electronic component according to the state of the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017]FIG. 1 shows a conductor strip 1 which, for example, consists of a copper alloy and is punched or etched out in a known fashion from thin sheet metal.

[0018] Also by punching or etching, a large number of connection pins 2 with bond surfaces 3 and assembly surfaces 4 a, 4 b, and 4 c for electronic or optoelectronic semiconductor components 5 a, 5 b, and 5 c are formed. The semiconductor components 5 a, 5 b, and 5 c—by means of an adhesion material such as for example a solder or a conducting adhesive—are attached material-positively to the assembly surfaces 4 a, 4 b, and 4 c of the conductor strip 1.

[0019] The semiconductor component 5 a, for example, is an optoelectronic transmitter, semiconductor component 5 b, for example, is an optoelectronic receiver, and the semiconductor component 5 c, for example, is an integrated circuit for processing the electric signals output by the optoelectronic receiver 5 b. The semiconductor components 5 a, 5 b, and 5 c are connected to one another, or with the bond surfaces 3 of the connection pins 2, by means of thin bond wires 6 made up of an aluminum or gold alloy.

[0020] Furthermore, the conductor strip 1 features a frame 8 with an inner boundary 8′ and frame sections 8.1 and 8.2. The frame section 8.2 is provided with a positioning and transport aperture 7 in the form of a round hole, and frame section 8.1 is provided with apertures 9 in the form of longitudinal holes, with lands 21 being located between the apertures 9. In addition, frame section 8.1 features a widening 10. The meaning and purpose of the apertures 9, lands 21, and widening 10 are described below.

[0021] During the mold process, frame 8 is located between the top and bottom sections of the mold form. Its inner boundary 8′ here runs around the mold form proper, as it has a slightly larger diameter than the later housing 12 (FIG. 2a, b) produced by the mold form.

[0022] The FIGS. 2a and 2 b show an as yet uncompleted electronic component 11 consisting of the assembly shown in FIG. 1 for the directed bidirectional optical data transmission at a later stage of production. Such a component 11 is also designated as a transceiver (from Transmitter and Receiver). In order to produce a protective housing 12, the semiconductor components 5 a-c (FIG. 1) and the bond wires 9 (FIG. 1) were envelopped with a thermoplastic synthetic material such as a synthetic resin (transparent for a specific wavelength range) by means of a mold process.

[0023] Here the housing 12 consists of two sections: a first housing section 12 a with a recess 13 (into which the connection pins 2 protrude later, FIG. 4) and a second housing section 12 b. From the plane between the two housing sections 12 a and 12 b, there protrude the parts of conductor strip 1 that have not yet been removed. The first housing section 12 a is the side of component 11 facing a printed circuit board (assembly side); the second housing section 12 b contains the two bulges 14 a or 14 b, which are arranged as lenses before transmitter 5 a (FIG. 1) or receiver 5 b (FIG. 1).

[0024]FIG. 3 shows a side view of the electronic component 11 according to FIGS. 2a and 2 b during a subsequent production step. Parts of conductor strip 1 that are no longer required are removed by punching or cutting, and thus, for example, the connection pins 2 are shortened to their final length.

[0025] In the case of components according to the state of the art, the frame 8 of conductor strip 1 features a distance to housing 12, which is why it is that during molding a mold material ridge (synthetic resin) forms, which later can only be somewhat reduced at great effort and cost but not completely removed, thus causing major difficulties during take-up by an assembly machine (FIG. 5).

[0026] The invention, however, provides for the frame 8—with its inner boundary 8′ to be directly adjacent to the area of the later housing 12, even protruding somewhat into the area of the later housing 12, so that the formation of a ridge at this point is prevented; this is the purpose of the widening 10 of frame section 8.1.

[0027] In order to be able to take out component 11 from the parts of conductor strip 1 that have not yet been removed, for example by pressing out with a small lever press, without this being prevented by the widening 10 of conductor strip 1 possibly protruding into housing 12 or housing 12 being damaged thereby, the conductor strip 1 is held by means of a holding device 15 in the area of frame section 8.1, and frame section 8.1 is then re-shaped mechanically, for example by embossing, such that a deformation 16, such as shown here for example in the form of a V-shaped bead, is produced.

[0028] It is advantageous if frame section 8.1 is provided with apertures 9, for example in the form of longitudinal holes. These longitudinal holes 9 weaken the material of frame section 8.1, such that the deformation 16 can be produced at reduced force and exactly along the lands 21 between these longitudinal holes 9.

[0029] By producing the deformation 16 the frame section 8.1 is pulled away from the housing 12 (in an ideal case) or, in a case which is not ideal, drawn out from housing 12, thus creating at that point a narrow and flat recess (groove) 17. The expert with relevant training will know that, instead of the V-shaped bead shown here it is possible to produce for example a U-shaped bead or any other mechanical deformation 16 in any given fashion such that frame section 8.1 will be deformed, thus creating an intermediate space between frame section 8.1 and housing 12.

[0030] The ideal case occurs if the widening 10 of frame section 8.1 and housing 12 are still just about in contact. If, in a non-ideal case, the widening 10 of frame section 8.1 is somewhat wider or if the housing 12 is somewhat offset during molding or produced to a somewhat larger size, then frame section 8.1 will in some small measure protrude with the widening 10 into the housing 12. When producing the deformation 16, the above-mentioned recess 17 is created in housing 12 by drawing out frame section 8.1 from the housing 12.

[0031] However, such a recess 17 only represents a minor “appearance defect” and does not have any further negative effects, as even in spite of a recess 17 a suction needle 18 (FIG. 4) will connect flush to the housing 12, and as the recess 17, which has the effect of a thin, flat channel running across the relevant surface area of housing 12, will only cause a very low volume of external air to be drawn in. This only leads to an almost unnoticeable force reduction by means of which such a component 11 is taken up by the suction needle 18 (FIG. 4). However, there will not be any tilting of component 11.

[0032]FIG. 4 shows the electronic component 11 finished in accordance with the process stated by the invention. The connection pins 2 are bent and protrude into the recess 13. The remaining parts of conductor strip 1 arranged outside the housing 12, in particular frame 8, have been removed. The suction needle 18 of an automatic assembly machine (not shown here) can now take up, by suction, component 11 on the smooth surface area opposite to the assembly side of housing 12 without any difficulty, securely hold and exactly place the same onto a printed circuit board, for example, without any possible recess 17 having any negative effect.

[0033] Finally, FIG. 5 shows a molded electronic component 20 according to the state of the art. A ridge 19 on the surface area opposite to the assembly side, which is formed during molding in the separation surface area of the mold tool between the housing sections 12 a and 12 b, causes a distance to appear between the suction needle 18 and the housing 12, such that the component 20 is not held at all or with reduced force and in tilted fashion only. In an unacceptably large number of cases, this has the consequence that the component 20 assumes a tilted position on suction needle 18, for example one of the mis-positions 23 or 24 shown here, and is thus imprecisely positioned on the printed circuit board, necessitating manual and thus costly reworking. Furthermore, another consequence frequently is that the component 20 is not taken up or is lost during transportation.

[0034] The device and the process according to the invention provide for the ridge-free production of such surfaces of an electronic component which serve as docking surfaces for the suction needle of an assembly machine. 

What is claimed is:
 1. A conductor strip arrangement for a molded electronic component (11) where at least one semiconductor element (5 a-c) is located on an electrically conducting conductor strip (1), and where around the conductor strip (1) and the at least one semiconductor element (5 a-c) a housing (12) made of a molding material is arranged such that there are still sections (8) of the conductor strip (1) outside the housing (12), wherein sections (8.1) of the conductor strip (1) feature a widening (10) such that these widened sections (8.1) of conductor strip (1) are directly adjacent to the later housing (12) or even protrude somewhat into the housing (12) in order to prevent a mold material ridge (19) from forming on the housing (12).
 2. A conductor strip arrangement according to claim 1, wherein the widened sections (8, 8.1) of the conductor strip (1) feature apertures (9).
 3. A conductor strip arrangement according to claims 1 or 2, wherein lands (21) are located between the apertures (9).
 4. A conductor strip arrangement according to claims 2 or 3, wherein the apertures (9) are implemented as longitudinal holes.
 5. A process for molding a housing (12) of an electronic component (11) in a mold form, with the component (1) featuring an electrically conducting conductor strip (1) and connection pins (2) located to one side, and the conductor strip (1) having a frame (8) with frame sections (8.1, 8.2), which forms the lateral boundary between the top and bottom sections of the mold form and whose diameter essentially is slightly larger than the diameter of the actual mold form, wherein a frame section (8.1) features a widening (10) directly adjacent to the mold form or even protruding somewhat into the mold form in order to prevent the formation of a mold material ridge (19) on housing (12).
 6. A process according to claim 5, wherein the at least one semiconductor element (5 a-c) is mounted on the conductor strip (1) by means of solder or an electrically conducting adhesive.
 7. A process according to claims 5 or 6, wherein the at least one semiconductor element (5 a-c) and the conductor strip (1) are contacted through electrically by means of bond wires (6) made of an aluminum or gold alloy.
 8. A process according to one of the claims 5 to 7, wherein the housing (12) is manufactured from a synthetic material transparent within a specific wavelength range.
 9. A process according to one of the claims 5 to 8, wherein, in a further production step, the widening (10) of conductor strip (1) reaching direct up to housing (12), or even protruding somewhat into the same, is mechanically deformed and thus removed from or out of the housing (12).
 10. A process according to claim 9 wherein the mechanical deformation of the conductor strip section (8.1) is achieved by means of embossing a deformation (16).
 11. A process according to claim 10, wherein the embossing of the deformation (16) is facilitated by providing apertures (9) in the sections (8.1) of the conductor strip (1).
 12. A process according to one of the claims 9 to 11, wherein the deformation (16) is manufactured as a bead.
 13. A process according to one of the claims 9 to 12, wherein the deformation (16) is manufactured as a V-shaped bead. 